Engine exhaust systems comprising a loudspeaker and methods of generating a drive signal for this loudspeaker are known. They are used, for example, in vehicles comprising a combustion engine and serve for adapting the noise emitted from the combustion engine to the surroundings. This allows to build the sound of an engine in the surroundings of the vehicle. In doing so, an amplification or an alteration of the engine noise as well as a reduction of the engine noise can be achieved. It is also known to play back the engine noise into the interior of the vehicle via loudspeakers in order to be able to build the sound of an engine in the passenger cell as well.
The loudspeaker is usually driven by a drive signal such that it generates a noise which resembles that of an engine, in the following referred to as an additional sound. The additional sound is superimposed in the exhaust system or the passenger cell to the engine noise, generating the sound of the engine which is emitted to the surroundings or perceived by the occupant.
The drive signal for the loudspeaker is designed here such that the sound of the engine emitted to the surroundings or perceived by the occupants is pleasant and adapted to the respective car. As a rule, a predefined source signal is used as the drive signal corresponding to the driving situation or the current operating parameters of the engine such as the rotational speed, said source signal consisting of a sequence of samples, for instance.
However, a free sound configuration of the engine sound, such as the reproduction of measured sounds, a free variation of the spectra over the rotational speed and load of the engine, is not possible here. It is likewise not possible to combine these source signals with an anti-sound function in which the noise of the engine is reduced by sound waves generated by the loudspeaker which are opposite in phase.
It is the object of the invention to provide a method of generating a drive signal as well as an exhaust system which allows a free sound configuration of the engine sound on the basis of a predetermined source signal as well as the use of the source signal with an anti-sound function of the exhaust system.